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a universe with no eyes

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does it need visible light

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the entire electromagnetic spectrum

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runs from gamma rays to radio waves

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spanning about twenty orders of magnitude

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and your eyes

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catch only a sliver worth zero point zero zero three five percent of it

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in other words

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if you imagine the whole spectrum

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as a flight route from Beijing to New York

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the part your eyes can see

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is about as long as shifting once in your seat

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hey there

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hello everyone

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I am Leo Wang

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today I want to talk about a question I keep chewing on

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on the surface it looks like a physics question

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but the deeper you go

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the more it points at the design logic under the universe

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and the question is this

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what is visible light really

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if there were no sentient beings

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no life that could see anything at all

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would the universe still need visible light

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do not answer too fast

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let us take the words visible light apart first

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the word light

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in physics means electromagnetic radiation

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and radiation is an oscillation of the electromagnetic field

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described exactly by the Maxwell equations

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from gamma rays at the highest frequency

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down to X rays and ultraviolet

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the sliver we can see infrared and microwaves

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all the way to radio waves at the lowest frequency

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physically they are exactly the same thing

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field oscillations traveling through space

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no band is more special than any other

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gamma rays are not superior to radio waves

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infrared is not inferior to ultraviolet

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the only difference between them

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is frequency and wavelength

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that is all

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so

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what about the word visible

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pay attention here

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it does not describe a physical property of light

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that word

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describes a relationship

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between radiation and one particular biological sense organ

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to put it bluntly

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the label visible

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was not put there by light

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it was put there by human eyes

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think about what that means

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in the entire framework of physics

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radiation from 380 to 700 nanometers

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has no intrinsic reason to be called light

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we call it light

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only because a carbon based creature happened to

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on an ordinary planet beside an ordinary star

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evolve a protein molecule that reacts

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electrochemically to that band of wavelengths

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that protein is called rhodopsin

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at its core sits a light sensitive small molecule

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when a photon of the right band hits that molecule

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its shape flips in one precise motion

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from bent to straight

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that tiny geometric change sets off a chain of reactions

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which finally becomes a nerve signal

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this is not some cosmic necessity

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it is the result of a string of evolutionary accidents

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and from the view of quantum field theory

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the photon itself is a deeply strange thing

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a photon has no mass

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it always moves at the speed of light

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and it does not experience time

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by the time dilation formula in special relativity

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as speed approaches the speed of light

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time approaches zero

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strictly we cannot define a rest frame for a photon

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but that mathematical limit hints at something wild

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for the photon

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if it had any experience at all

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leaving the sun and striking your retina

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are separated by no time at all

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the whole universe is compressed for it

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you think you are looking at light

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but light does not travel inside time

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the tool you use to see the world

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is itself something that does not live in time

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why are human eyes tuned to exactly this band

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there is a widely repeated explanation

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the peak of solar radiation sits near 500 nanometers

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right in the middle of visible light

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so evolution aimed our eyes at the brightest spot

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it sounds perfectly reasonable

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but it is actually wrong

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physicists have run the numbers

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the solar peak depends on whether you plot wavelength or frequency

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plot by wavelength

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and the peak sits at 500 nanometers

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inside the visible range

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plot by frequency

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and the peak sits at 880 nanometers

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out in the near infrared

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so the claim that the solar peak lands in the visible

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is an illusion created by your choice of axis

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the real reason is far more interesting

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scientists found

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that the key factor deciding what band we see

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is water

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the transparency window of liquid water

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lands exactly on the visible band

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water absorbs heavily in the infrared

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and in the ultraviolet too

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but between 380 and 700 nanometers

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water is relatively transparent

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when the first photoreceptors evolved in the ocean

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they could only use the wavelengths water let through

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in other words

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our eyes did not choose visible light

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water chose visible light

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and our eyes simply followed the water

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that alone is worth sitting with

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but the more interesting part is still ahead

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if you asked a mantis shrimp

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what visible light is

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you would get a completely different answer

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a mantis shrimp has 16 kinds of photoreceptors

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humans have only three

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it sees deep ultraviolet down to 300 nanometers

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and far red out to 720 nanometers

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it can even see polarized light

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the direction in which the wave vibrates

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which barely exists for human eyes

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for a mantis shrimp

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our visible light is just a subset of its world

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now look at snakes

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many pit vipers carry infrared pit organs on the face

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which sense thermal infrared radiation

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in the perception of a snake

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a warm blooded body glows in the dark

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for a snake

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infrared is visible

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bees can see ultraviolet

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many flowers carry ultraviolet patterns we cannot see at all

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like landing strips painted for bees

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for a bee

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the red flowers we see are nearly black

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while the ultraviolet nectar guides blaze

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do you see the problem

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the concept of visible light

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means something completely different

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for every different species

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no version of it is more correct than another

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or more objective

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every kind of eye is a different filter

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turning one radiation field into a different visual reality

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in other words

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visible

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is not a property of light

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it emerges from consciousness meeting matter

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and there is a deeper reversal hiding here

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we assume humans are the ones observing the universe

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but from an evolutionary view

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physical conditions shaped how the observer observes

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water transparency set the range of the eye

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atmospheric scattering set the color of the sky

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the solar spectrum set the color of plants

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and plant color drove primates toward three color vision

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because apes that spotted red fruit among green leaves

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found more nutrition

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and were more likely to survive

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so the colorful world you see

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is not the world as it is

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it is a survival interface

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custom built for you by billions of years of selection

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you think you are seeing the truth

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you are reading a heavily edited summary

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this reminds me of a very precise Buddhist framework

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called the three natures

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we covered it in an episode on the Samdhinirmocana Sutra

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Yogacara holds

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that all phenomena have three layers

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the first is the imputed nature

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the labels and concepts our minds impose

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the second is the dependent nature

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the actual relations arising from causes and conditions

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the third is the perfected nature

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what remains when every label and bias is stripped away

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the concept of visible light

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lands exactly on the imputed nature

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it is a human label stuck onto radiation

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what actually happens is the dependent nature

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photons of one wavelength meet one visual protein

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trigger one specific chemical reaction

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produce one specific nerve signal

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and the brain weaves that into the experience of color

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while the radiation itself

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just keeps oscillating there

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it does not care who is watching

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or whether anyone is watching at all

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that is the perfected nature

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speaking of color

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there is an even harder fact to face

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color

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does not exist in the physical world

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this is not philosophical speculation

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it is a hard result from neuroscience

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the physical world holds only radiation at different frequencies

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a 500 nanometer wave is not green

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it is a field oscillating 600 trillion times a second

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green

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is what your brain does after the cone cells in your retina fire

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a subjective experience it invents on its own

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no equation in physics has a variable for that experience

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philosophy has a term for this

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qualia

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what red looks like

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what pain feels like

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the raw quality of these experiences

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is territory the equations cannot reach

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physics can describe the wavelength of a photon exactly

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its energy momentum and polarization

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but physics can never tell you

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why when that photon hits your retina

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you experience red instead of green

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or nothing at all

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David Chalmers called this the hard problem of consciousness

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all research on how the brain processes information

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belongs to the easy problems

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the hard problem is this

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why is any of that processing accompanied by experience

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why does it not just run silently in the dark

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try a small experiment and you will feel it

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close your eyes for three seconds

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then open them

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while your eyes were closed

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the lamp in the room was still on

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radiation was still bouncing around the room

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but your world went dark

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you open your eyes

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and the world lights up again

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so tell me

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what actually changed

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not the light

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the light was there the whole time

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what changed was your perception channel switching

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bright and dark are not physics concepts

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they are experience concepts

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light is never bright

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and never dark

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bright and dark

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are whispers your mind says to radiation

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the equations of physics cannot hear them

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now

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let us go back to the opening question

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if the universe held no sentient beings

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no perceiver of any kind

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would it still need visible light

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strictly speaking

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in a universe without observers

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the concept of visible light does not exist

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there are only fields oscillating by the Maxwell equations

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no wavelength is marked as visible

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and no frequency produces color

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the whole universe is a colorless silent tasteless mathematical structure

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temperature is just a statistic of molecular motion

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not the feeling of heat

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sound waves are just periodic changes in air density

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not the experience of loudness

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a universe without observers

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can run perfectly well on physics alone

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the Maxwell equations hold without any eyes

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gravity bends spacetime with nobody to feel it

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stars fuse without an audience

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but here a very subtle problem appears

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quantum mechanics tells us

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that before measurement

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particles sit in superposition

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one photon takes two paths at once

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one electron sits in several energy levels at once

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only when measurement happens

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does the superposition collapse into one definite result

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the physicist John Wheeler had a famous thought experiment

286
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the delayed choice experiment

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and in 2007

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French scientists actually ran it in the lab

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the result is deeply counterintuitive

290
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before you measure

291
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which path the photon took

292
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has no definite answer at all

293
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some read this as saying

294
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that your choice of measurement now

295
00:12:04,491 --> 00:12:07,033
can affect what the photon did in the past

296
00:12:07,303 --> 00:12:10,063
late in life Wheeler proposed a very bold conjecture

297
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the participatory universe

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he drew a famous sketch

299
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a universe shaped like a U

300
00:12:14,904 --> 00:12:16,823
one end is the big bang

301
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the other is a huge eye watching that beginning

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00:12:20,544 --> 00:12:21,502
his point was this

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00:12:21,504 --> 00:12:23,832
the observer is not a bystander to the universe

304
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the observer helps create the universe itself

305
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including its past

306
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without an observer

307
00:12:29,103 --> 00:12:30,712
there is no definite history

308
00:12:30,864 --> 00:12:32,143
if Wheeler was right

309
00:12:32,144 --> 00:12:35,823
the question is no longer whether an eyeless universe needs light

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it becomes

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whether a universe without observers

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00:12:37,943 --> 00:12:40,245
can ever become a definite universe

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00:12:40,436 --> 00:12:42,845
this brings up a striking image

314
00:12:43,236 --> 00:12:44,286
picture this

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00:12:44,436 --> 00:12:48,526
the first hundred million years after the big bang

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the universe held only hydrogen and helium

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no planets

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no water

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no life

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and it was packed with electromagnetic radiation

321
00:12:56,476 --> 00:12:57,885
photons flying everywhere

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but not one of them was visible

323
00:13:00,677 --> 00:13:03,166
no beam of light was red or blue

324
00:13:03,557 --> 00:13:05,526
physically the universe was extremely busy

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00:13:05,637 --> 00:13:07,765
but experientially it was completely blank

326
00:13:08,157 --> 00:13:10,005
a theater with no audience

327
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every actor is present

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00:13:11,757 --> 00:13:14,845
lights sound and sets all ready

329
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but every seat is empty

330
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those photons flew for billions of years

331
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until the first eyes opened in some primordial sea

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00:13:24,836 --> 00:13:28,206
and the universe first knew bright from dark

333
00:13:28,316 --> 00:13:29,926
and had color for the first time

334
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so look

335
00:13:31,165 --> 00:13:34,613
we started with what looked like a simple physics question

336
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what is visible light

337
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but peel it layer by layer

338
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and it touches physics biology neuroscience

339
00:13:42,165 --> 00:13:45,493
philosophy and every core puzzle of consciousness

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00:13:45,925 --> 00:13:47,454
the phrase visible light

341
00:13:47,484 --> 00:13:49,973
looks like it describes a physical phenomenon

342
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but in fact

343
00:13:51,045 --> 00:13:54,694
it quietly leaks the deepest secret of the universe

344
00:13:54,805 --> 00:13:55,314
and it is this

345
00:13:55,604 --> 00:13:57,643
every reality you experience

346
00:13:57,645 --> 00:13:59,213
is not reality itself

347
00:13:59,244 --> 00:14:03,294
it is a translation emerging where mind meets matter

348
00:14:03,925 --> 00:14:05,843
the colors you see are translation

349
00:14:05,844 --> 00:14:07,774
the sounds you hear are translation

350
00:14:07,885 --> 00:14:10,133
the hardness you touch is translation

351
00:14:10,324 --> 00:14:11,434
translation needs two things

352
00:14:12,045 --> 00:14:13,654
a source text and a translator

353
00:14:14,005 --> 00:14:15,814
radiation is the source text

354
00:14:15,925 --> 00:14:17,654
your consciousness is the translator

355
00:14:17,844 --> 00:14:18,674
without a translator

356
00:14:18,925 --> 00:14:20,363
the source text still exists

357
00:14:20,364 --> 00:14:22,971
but it never becomes any experience

358
00:14:23,122 --> 00:14:24,790
so does the universe need visible light

359
00:14:25,362 --> 00:14:26,971
the universe needs nothing

360
00:14:27,482 --> 00:14:31,251
the word need already assumes a subject with intent

361
00:14:31,482 --> 00:14:33,960
fields and particles running on equations

362
00:14:33,962 --> 00:14:35,771
have no such thing as needing

363
00:14:36,002 --> 00:14:37,131
but turn it around

364
00:14:37,202 --> 00:14:40,611
if no observer had ever appeared in the universe

365
00:14:40,641 --> 00:14:42,950
would the word exist still mean anything

366
00:14:43,641 --> 00:14:45,731
a tree falls in a forest

367
00:14:45,761 --> 00:14:47,680
if no living thing hears it

368
00:14:47,681 --> 00:14:48,751
did it make a sound

369
00:14:49,322 --> 00:14:51,531
this is not a boring philosophical riddle

370
00:14:51,602 --> 00:14:56,011
it is the core puzzle of quantum mechanics in everyday words

371
00:14:56,866 --> 00:14:57,255
maybe

372
00:14:57,586 --> 00:14:59,314
the phrase visible light

373
00:14:59,346 --> 00:15:01,035
is really telling us this

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00:15:01,106 --> 00:15:03,434
the existence of the universe and of consciousness

375
00:15:03,466 --> 00:15:05,035
are two faces of one thing

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00:15:05,346 --> 00:15:07,755
light does not need to be seen to exist

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00:15:07,825 --> 00:15:09,674
but the act of seeing

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00:15:09,706 --> 00:15:14,355
turns abstract equations into a living experience

379
00:15:14,545 --> 00:15:16,594
consciousness is not a bystander to the universe

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00:15:16,665 --> 00:15:19,523
it is how the universe knows itself

381
00:15:19,793 --> 00:15:20,342
think about it

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00:15:20,834 --> 00:15:23,042
13 point 8 billion years of cosmic evolution

383
00:15:23,114 --> 00:15:25,072
from the big bang to hydrogen atoms

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00:15:25,074 --> 00:15:26,302
to fusion inside stars

385
00:15:26,594 --> 00:15:28,113
to the forging of heavy elements

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00:15:28,114 --> 00:15:29,513
to planets condensing

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00:15:29,513 --> 00:15:30,763
to oceans appearing

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00:15:30,793 --> 00:15:35,202
to the first light sensitive protein folding by chance in a cell

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00:15:35,273 --> 00:15:38,153
to that protein being struck by its first photon

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00:15:38,153 --> 00:15:39,842
and firing the first electrical signal

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00:15:39,994 --> 00:15:40,422
in that moment

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00:15:40,714 --> 00:15:42,763
the universe saw itself for the first time

393
00:15:43,474 --> 00:15:45,023
13 point 8 billion years of waiting

394
00:15:45,313 --> 00:15:46,802
all for that single act of seeing

395
00:15:47,891 --> 00:15:50,040
so does the universe need visible light

396
00:15:50,611 --> 00:15:52,170
maybe the real answer is this

397
00:15:52,172 --> 00:15:53,941
the universe does not need visible light

398
00:15:54,452 --> 00:15:56,341
but the universe needs to be seen

399
00:15:56,771 --> 00:15:57,481
and visible light

400
00:15:57,812 --> 00:15:59,861
is only one of the ways it reaches that

401
00:15:59,971 --> 00:16:01,120
on this planet

402
00:16:01,412 --> 00:16:03,130
through these carbon based creatures

403
00:16:03,131 --> 00:16:04,861
one solution among many

404
00:16:05,212 --> 00:16:06,540
on other worlds

405
00:16:06,572 --> 00:16:10,500
silicon life may see the universe in X rays

406
00:16:10,812 --> 00:16:12,181
and at a deeper level

407
00:16:12,212 --> 00:16:16,660
consciousness may be the ultimate organ the universe sees itself with

408
00:16:16,891 --> 00:16:19,020
bound to no particular wavelength

409
00:16:19,052 --> 00:16:21,701
limited to no particular sensory channel

410
00:16:22,083 --> 00:16:25,013
we humans carry a deep rooted illusion

411
00:16:25,124 --> 00:16:27,692
that what we see is the objective world

412
00:16:27,884 --> 00:16:28,553
but think about it

413
00:16:28,884 --> 00:16:30,962
a mantis shrimp feels the same way

414
00:16:30,963 --> 00:16:33,003
a pit viper feels the same way

415
00:16:33,004 --> 00:16:35,013
a bee feels the same way

416
00:16:35,164 --> 00:16:38,533
each one is certain that it sees reality

417
00:16:38,723 --> 00:16:41,572
yet none of them sees the same world

418
00:16:41,764 --> 00:16:43,472
so who sees the real one

419
00:16:43,963 --> 00:16:44,793
the answer may be

420
00:16:45,164 --> 00:16:47,173
that nobody does

421
00:16:47,563 --> 00:16:48,763
every kind of vision

422
00:16:48,764 --> 00:16:51,653
is one face of the universe shown

423
00:16:51,723 --> 00:16:53,612
through one particular biological filter

424
00:16:54,244 --> 00:16:56,253
like a many sided crystal

425
00:16:56,364 --> 00:16:59,452
each angle refracts completely different light

426
00:16:59,683 --> 00:17:02,773
and no angle shows you the crystal itself

427
00:17:03,521 --> 00:17:05,249
right now you are watching this video

428
00:17:05,600 --> 00:17:06,910
photons from the screen

429
00:17:07,120 --> 00:17:08,160
cross the air

430
00:17:08,161 --> 00:17:09,650
land on your retina

431
00:17:09,761 --> 00:17:12,249
flip the shape of rhodopsin

432
00:17:12,320 --> 00:17:13,349
trigger an electrical signal

433
00:17:13,680 --> 00:17:15,129
that travels to your visual cortex

434
00:17:15,320 --> 00:17:19,730
and your brain weaves it into images color words and meaning

435
00:17:20,201 --> 00:17:21,599
through this entire process

436
00:17:21,600 --> 00:17:25,209
every step can be described exactly by physics and biology

437
00:17:25,360 --> 00:17:26,230
but one thing

438
00:17:26,561 --> 00:17:28,689
no equation can explain

439
00:17:28,840 --> 00:17:29,310
and it is this

440
00:17:29,521 --> 00:17:31,230
why do you experience any of it

441
00:17:31,721 --> 00:17:36,089
why is it not a precise machine crunching data silently in the dark

442
00:17:36,120 --> 00:17:37,849
why is there a you here seeing

443
00:17:37,880 --> 00:17:38,310
hearing

444
00:17:38,561 --> 00:17:39,189
and thinking

445
00:17:40,360 --> 00:17:41,109
that why

446
00:17:41,400 --> 00:17:44,570
is the door that this plain little idea of visible light

447
00:17:44,600 --> 00:17:46,570
is really knocking on

448
00:17:47,521 --> 00:17:48,191
what do you think

449
00:17:48,601 --> 00:17:49,991
if the universe had no eyes

450
00:17:50,242 --> 00:17:51,511
would it still count as existing

451
00:17:52,002 --> 00:17:54,610
share your thoughts in the comments

452
00:17:54,761 --> 00:17:55,431
I am Leo Wang

453
00:17:55,642 --> 00:17:56,613
see you next time